Preliminary results have identified no “bad toxins” in the mystery substance that was injected into a U.S. air marshal in an attack at a Nigerian airport late Sunday, the FBI said today.

FBI spokesperson Christos Sinos told ABC News that the air marshal, who has not been identified, remains under observation, but initial tests of the remaining contents of the syringe found it negative for toxins including Ebola.

U.S. officials told ABC News Monday that an air marshal had been stabbed in the arm with a syringe in the international airport in Lagos, Nigeria the night before. While the attacker managed to get away, the air marshal was able to recover the syringe and continue his flight with other marshals to Houston. He was met at the airport early Monday morning by FBI and Centers for Disease Control (CDC) officials where he was subject to an on-site medical screening and then transported to a local hospital for observation, officials said.

However Jon Adler, the National President of the Federal Law Enforcement Officers Association, told ABC News that while the results of the preliminary tests are “encouraging… there’s still more medical due diligence to be performed in the testing.” The air marshal too has not shown any symptomatic reaction to the incident, Adler said.

In an interview with ABC News Adler said yesterday’s attack on a Federal Air Marshal in the Lagos airport did not appear to be a random act. “Our air marshals involved in the incident were absolutely convinced it was a deliberate attack,” he said.

When the team of air marshals arrived at the Lagos airport, their usual Nigerian “expeditor” was not on hand to escort them through the notoriously crowded terminal and the air marshal team noted a group of “suspicious men” observing them, Adler recounted. In the chaos of the crowd the men were separated when one of the marshals was stuck in the back of the arm with the syringe, he said.

Adler said it was unclear if the attackers knew the men were U.S. law enforcement officials, diplomats or American travelers.

“Hopefully those involved in the investigation will determine if there are any links between known terrorist groups or if these are just a bunch of amateur lone weasels functioning in a sort of reckless, lethal manner,” Adler said.

FBI spokesman Sino confirmed they were investigating reports of a suspicious group being involved in the attack but said that unfortunately so far, an examination of closed circuit footage from the airport had not proved helpful in identifying the attackers.

Adler said the officer could spend up to another three weeks under observation – which in medical terms is a step below isolation, a recourse taken when a patient becomes symptomatic for a contagious illness.

“We hope the results come back favorably” said Adler, who criticized what he said was a complete lack of police response by the Nigerian authorities. “That’s very disconcerting and that’s something that I hope the state department steps up their game and intervenes and find out why there was no cooperative support when this incident transpired.”

U.S. State Department spokesperson Marie Harf told reporters today that Nigerian authorities were “jointly investigating” the case with the U.S. law enforcement and are “fully cooperating.”

Along with neighboring West African nations, Nigeria has been battling an outbreak of the Ebola virus that has claimed more than 2,000 lives in the region.

[Editor’s Note: An earlier version of this report said the CDC carried out the tests on the substance in the syringe. The FBI said the CDC transferred the substance to the National Bioforensic and Analysis Center at Ft. Detrick in Maryland.]